Solution : https://service.sap.com/sap/support/notes/765763 (SAP Service marketplace login required)
Summary : 
      When downloading text data with gui_download in SAP GUI, the default codepage follows the SAP GUI session codepage, potentially leading to compatibility issues with applications like Microsoft Excel that may not support UTF-8 when connected to a Unicode system. To address this, SAP GUI now allows users to specify their preferred codepage in the SAPLogon dialog's advanced properties. The enhanced functionality includes two default settings: ANSI for Unicode systems, which aligns with the login language but poses risks of character corruption for unsupported Unicode characters, and UTF-8 for uniformity across systems. These settings require the SAP GUI 6.40 Patch 3 and specific support packages for SAP systems 6.20 and 6.40.
Key words : 
solution sap gui, sap gui codepage, ansi codepage matching, required support packages, sap system releases 6, downloaded text file, default codepage, file dialog, applications support, specific codepage
Related Notes : 
       
| 1319517 | Unicode Collection Note | 
| 1088209 | Help for troubleshooting: Code page display problems | 
| 872785 | Incorrect code page for Word download in Unicode systems | 
| 855367 | LAW: Problems with UNICODE/non-UNICODE systems | 
| 508854 | SAPGUI: How to use Unicode |